Fuel tanks on board vehicles of various kinds must generally meet sealing and permeability standards in relation to the type of usage for which they are designed and the environmental requirements with which they must comply. Both in Europe and throughout the world we are currently experiencing a considerable tightening of the requirements concerned with limiting the emissions of pollutants into the atmosphere and into the environment in general.
To limit these emissions, care is taken in particular to position the accessories (ventilation lines, valves, baffles, stiffeners, etc.) inside the tank and, to limit the number of openings through its wall, the Applicant has developed a method of initially molding a parison that includes at least one slot for introducing thereinto (and fastening thereto) accessories during the actual molding of the tank and thus avoiding drilling openings (see, in particular, Application EP 1 110 697).
The Applicant has also developed a particular method for this fastening (in situ snap-riveting, the subject of Application WO 2006/008308, the content of which is, for this purpose, incorporated by reference into the present application) and also improvements that are respectively the subject of international Applications WO 2007/093573 and PCT/EP 2008/059042 in the name of the Applicant, the content of which is also incorporated by reference into the present application.
The object of the aforementioned Application WO 2007/093573 is to provide a process that allows an accessory to be incorporated into a plastic fuel tank during its manufacture by molding, without generating deformations after the tank has cooled, when the accessory is fastened thereto. In this process, the accessory is provided, at least one of its fastening points, with a fastening part such that, although the accessory is fastened to the wall of the tank, it can move relative to the corresponding fastening point on the wall of the tank.
Although this approach makes it possible to solve the deformations generated by the differential shrinkage of the accessory and of the tank during post-molding cooling, the Applicant has however observed the formation of a hollow (depression or concave relief when seen from outside the tank, convex relief when seen from the inside) in the wall of the tank and to the right of the location where the accessory is fastened. Moreover, depending on the geometry of the accessory, the Applicant has also noticed in certain cases the appearance of beads of material trapping at least one portion of the accessory in the wall of the tank, which adversely affects the aforementioned mobility and the homogeneity of the parison (with leakage risks that result therefrom).